Earlier this week, VICE ran an interview with the prominent HIV denialist Joan Shenton. But her crackpot theories aren't just laughable – they can be deadly.

It's been over 16 years since Joan Shenton published her highly controversial book, Positively False – Exposing the Myths Around HIV and AIDS. As one of the world's foremost critics on what she refers to as the "completely wrong" science of HIV and AIDS, her argument can basically be reduced to this: AIDS is a Big Pharma conspiracy and the drugs companies manufacturing the antiviral medications are, along with compliant governments, cooking up a big, stinking, witches-around-the-cauldron plot to keep themselves swimming in cash. But while she may describe herself as an HIV "dissident", a more appropriate word for Shenton – interviewed by VICE earlier this week – would be "denialist".

Where does this urge to deny the existence of HIV come from? According to Denying AIDS, psychologist Seth Kalichman's 2009 exposé of the AIDS denial movement, denialists across the world have all kinds of crackpot theories. Mainly, they seem to hinge on the belief that, one day, "orthodox" medical theories on HIV will "crumble". Denialists insist that antiretroviral medication is "toxic" and that there's no "proven link" between HIV and AIDS.

The problem is, the "science" that denialists like Shenton rely on is decades-old and largely founded on the beliefs of a man called Peter Duesberg, a cell biologist at the University of California, Berkeley, who, in 1987, wrote an extensive paper on how he believes HIV is "harmless" and does not cause AIDS. Since the 80s there has been consistent, empirical proof that denying this link is – as Yusef Azad, director of policy and campaigns at the National AIDS Trust, says – "scientific illiteracy".

Bollocks though it may be, the movement retains a dangerous traction. 2009 was a great year for AIDS denialists . In November of that year, a record number from around the world travelled to the Rethinking AIDS conference in Oakland, California. The headline "act" was a controversial new documentary called House of Numbers, which espoused denialistic theories. Only, it subsequently met such enormous backlash that, when the Spectator organised a debate and screening of the film, they had to cancel it after many of the speakers pulled out.

For all the outrage directed at people like Shenton, denialism can still have deadly consequences.

On her website, Shenton provides examples of the cases of Jody Wells and Huw Christie – the first two editors of the fringe magazine Continuum. Both decided to ignore the so-called "orthodox" medical advice, and they both ended up dead. "We're waking up to the truth and the more of us that survive and live on in health to beat the odds, the more the lie will be shown up for what it is," Wells wrote in 1994 – 16 months before he died, and just before new therapies vastly improved life expectancy for people with HIV. These new treatments saw so many young men who may have followed Wells' lead "rise from their deathbeds and go dancing", as Brian Deer – who wrote one of the first reports on AIDS in 1981 – put it.

Shenton also talks about a lady called Christine Maggiore, a woman from California who co-founded a group called "Alive and Well AIDS Alternatives". This was before her HIV-positive daughter died, aged three, of pneumonia and Christine herself died of the disease in 2008. However, in a subsequent podcast interview, Duesberg said: "big deal", and that it was "nothing" – despite pneumonia being a well-known complication of HIV infection.

Tom Hayes is Editor-in-Chief of Beyond Positive and living a full, healthy life as an HIV-positive man. After he criticised VICE's interview with Shenton for not challenging her enough, I reached out to him for comment: "I am the biggest proponent of free speech you'll find anywhere, and I have no desire to stop any denialist saying what they believe. But although HIV is, on the whole, a well-managed condition in the UK, the way people like myself are living with it can often take away from the seriousness of the situation." He tells me about writers on his team who, at various stages, have been drawn in by denialist theories and "faith healing" and only realised "when they ended up in hospitals and days away from death [...] what they'd done to themselves".

"One of my writers, James, approached a leader at a Christian Festival shortly after his HIV diagnosis. He was told that, if his faith was strong enough, that God would cure his HIV because 'nothing was too big' for God. They prayed together and James left feeling much more upbeat about his situation."

Only, James continued to pray, believing that it would heal him, and ignored calls from the HIV clinic to go and have his bloodwork done. Months later – and only after his health deteriorated – did he go back to the HIV clinic.

"It was then he found out that the HIV had been busy replicating," says Hayes. "James's viral load was sky high and his CD4 count [a measure of your immune system] was through the floor. Luckily, he came to his senses in time to receive the urgent care he needed to save his life."

Many others don't, though, and, as Hayes explains, "either end up with an AIDS or Late Stage HIV diagnosis. Some even die through their ignorance."

In the despair that comes with a new diagnosis, ignorance is born from a frantic need for answers, for hope. If someone tells you there's hope in another, less conventional direction, vulnerability can lead you down avenues that you'd never walk rationally. But while faith healers rely on the idea of some abstract, all-healing "It", AIDS denialists rely on phoney science.

When Shenton suggests that, because HIV can't be "purified", it doesn't exist, she is demonstratively wrong. HIV has been proven to exist many, many times – in fact, we now know the protein structure of the viral capsid. Every person with HIV who is diagnosed has had their viral load counted – this is done by counting the copies of HIV in a given blood sample. Blood taken from a human body is not capable of "fiddling the numbers" – unless every lab technician in every hospital across the world is in on the hoax, too. Maybe there's a giant manufacturer of biased pathology syringes out in the desert somewhere.

Shenton's theories on the antiretroviral drug AZT are also completely barking. AZT, as Hayes explains, isn't used in HIV medication any more. Some people who were prescribed it in the 1980s and 1990s are still alive ("one of them writes for me") and have chosen to remain on the medication because it works for them. It's just not prescribed to new patients.

Shenton's idea that HIV can be contracted through amyl nitrate (poppers) is also laughable. Those theories were widely rubbished in the 1990s. The bodily fluids that can transport the HIV virus are blood, semen, anal mucus, vaginal mucus, breast milk, cervical mucus and, in minute quantities, saliva. According to aids.gov, these body fluids "must come into contact with a mucous membrane or damaged tissue or be directly injected into your bloodstream (by a needle or syringe) for transmission to possibly occur".

When she asserts, as she does, that there is no chance of a heterosexual HIV epidemic ever occurring, you wonder if she's aware that 50 percent of the 107,000 estimated to be living with HIV in the UK are straight. Or, that the vast majority of people with HIV and AIDS in Africa (35 million), Russia (940,000) and Ukraine (210,000) are heterosexual, too. These aren't figures plucked from nowhere – they are real people, receiving treatment.

AIDS denialism tells anyone with a diagnosis – or someone with a newly-diagnosed friend or relative – what they want to hear: that HIV doesn't cause AIDS and that if you live a "healthy lifestyle", you won't get AIDS.

In fact, those with HIV are living long, full lives because of early detection and new and improved treatments. Countries that have launched vigorous testing and treatment programmes – like Brazil and Botswana – have reduced suffering, prolonged life and saved billions in healthcare costs. In places like South Africa, where testing and treatment programmes were stalled because of former President Thabo Mbeki's denialism, the result was 300,000 unnecessary deaths and over 35,000 infants infected with HIV. Harvard researchers quantified the death toll in a vast paper, but still, Mbeki kept a vow of silence. It must have been hard to find the words to express grief over 300,000 senseless deaths caused by your own dragging feet.

These stats aren't conjecture – they're death counts. Throughout the epidemic the evidence has, as science has advanced (and still advances), proven that HIV leads to AIDS and that antiretroviral drugs save and prolong lives. Will Harris, Head of Media at Terrence Higgins Trust, says that, although those who "refuse to listen" are "in the minority", the reason they're in the minority is because those living with HIV who buy into denialism will usually "stop taking their medication and die".

"Barmy conspiracy theories do nothing to help the 35 million people living with HIV worldwide, whereas access to antiretrovirals can," adds Harris. "People living with HIV already have to contend with enough stigma and misinformation around the virus, without having to deal with bare-faced lies."

Every kind of denialism is rhetorical. Whether it's Holocaust deniers arguing over the evidence for the Nazi's mass murdering of Jews, global warming denialists claiming that climatologists are all in constant disagreement about evidence like ice caps literally melting in front of people's eyes, or anti-vaxxers parroting the same nonsense "link" between MMR and autism, it all boils down to old, tinpot science that creates the illusion of genuine debate taking place among "experts" with differing, yet informed, opinions.

The reality, of course, is that you can't fight good science with bad science, and that the only thing HIV denialists like Shenton are experts at is distorting the truth.